Leaded vs. Unleaded

Leaded gasoline is basically an artifact of the past. Lead was added to gasoline at one time (prior to 1974) in order to boost octane and lubricate high temperature components like valves. This was necessary in the high compression engines of the time to prevent knock. Lead deposits that formed on the valve seats after combustion were also helpful in preventing wear and maintaining good cylinder compression and therefore engine performance.

However, the lead also found its way into the exhaust gas and polluted the air. Lead was determined to be poisonous, so leaded gasoline was eventually phased out over two decades in favor of unleaded gasoline. Furthermore, leaded gasoline was incompatible with the catalytic converters that were required to eliminate other forms of exhaust pollution. Leaded gasoline was totally banned and unavailable in the United States beginning in 1996. To compensate for the lack of lead deposits and their protective qualities, unleaded gasoline engines (1975 and later) have specially hardened valve parts that resist wear.

SYSTEMS
FUEL
GASOLINE VOLATILITY
OXYGENATED VS. REFORMULATED